Generally, a random access channel (RACH) is a channel for a user equipment (hereinafter abbreviated UE) to perform downlink synchronization with a base station and for finding base station information. A position of a corresponding channel and the like can be obtained from base station information. And, an RACH can be accessed while a UE is not synchronized with a base station. The larger a cell size gets, the longer a length of the RACH becomes. It is a matter of course that the RACH is used for a UE to match uplink synchronization. And, it is also a matter of course that the RACH is a channel having collision probability.
Meanwhile, if data communication is being carried out between a base station and a random UE, the UE has to report a control signal such as ACK/NACK for transmitted packets, CQ informations for scheduling, TF (transmission format) information for uplink transmission and the like to the base station.
Yet, if RACH is inserted in the course of performing the above process and if the RACH uses an entire system band width, the UE is beset with a difficulty in transmitting a control signal to the base station. In particular, since an RACH length increases in proportion to a cell size, a delay time taken for the UE to send a control signal to a base station is increased.
THE LTE currently discusses a scheme for transmitting a control signal carried on a predetermined area after TTI has been discriminated by FDM and a method of selecting specific OFDM symbol(s) to use for a control signal as a scheme for transmitting the above-explained control signal such as ACK/NACK and the like. If there exists data to be transmitted, a scheme for transmitting a control signal together with the data is taken into consideration. Yet, it has not been discussed how to handle a case that RACH is interrupted in the course of uplink transmission.
FIG. 1A and FIG. 1B are diagrams for a scheme for transmitting a control signal by FDM or TDM according to a related art.
Referring to FIG. 1A, a control signal is transmitted in a manner that a resource region for a control signal transmission is allocated to a predetermined frequency band like the shaded region ‘control signal region’ shown in FIG. 1A within 1 TTI (transmission time interval) corresponding to a transmission unit resource region in LTE.
Referring to FIG. 1B, a control signal is transmitted in a manner that a resource region for a control signal transmission is allocated to a predetermined time domain like the shaded region ‘control signal region’ shown in FIG. 1B within 1 TTI.
FIG. 2 is a diagram for a case of transmitting RACH on a control signal transmission band.
Referring to FIG. 2, RACH is assigned in the course of transmitting an uplink control signal in case that a whole system band is used. In this case, since a UE is unable to use an uplink at all, it is not able to deliver a control signal. And, all communication protocols are delayed as long as a length of the RACH.
Meanwhile, even if RACH fails to occupy a whole system bandwidth, RACH transmission is frequently allocated to be simultaneously carried out on each frequency band. In this case, like the case of FIG. 2, there is a problem that an uplink control signal transmission is delayed as long as a length of the RACH.
Therefore, a technique for transmitting a control signal efficiently in a section for transmitting RACH is demanded.